Technology in which a terminal structure is modified by utilizing a termination reaction in the last stage of polymerization, a functional group is directly added to a side chain, or a polymer is grafted to add a functional group is used as a technology of changing properties of natural polymer such as natural rubber, or a synthesized polymer (for example, PTLs 1 and 2 below).
However, regardless of solution polymerization or emulsion polymerization, a method of simply and easily introducing an alkoxysilyl group in a main chain structure or a molecular terminal by rearranging a main structure of a polymer is not yet obtained. Furthermore, in the conventional technology, a decrease in a molecular weight may unintentionally occur, and it is considered that the decrease adversely affects properties, depending on an object to be used.
Regarding a depolymerized natural rubber useful as an adhesive, a pressure-sensitive adhesive, a sealant, a caulking agent, a plasticizer and the like, it is disclosed in PTL 3 mentioned below to produce a liquid depolymerized natural rubber having a number average molecular weight of from 2,000 to 50,000 by air oxidation of a deproteinized natural rubber dissolved in an organic solvent in the presence of a metal catalyst to perform depolymerization. This PTL discloses that a molecular chain having a carbonyl group in one terminal and a formyl group in other terminal is formed by the decomposition of a main chain by air oxidation, and the formyl group is then recombined by aldol condensation, but does not disclose that the carbonyl group is recombined. Furthermore, in this PTL, depolymerization is conducted in a solution of an organic solvent, and it is not described that the recombination is performed by changing a system containing decomposed polymers into an acidic or basic system. Furthermore, the production method is to obtain a telechelic liquid rubber having carbonyl groups in both terminals, has an object to obtain a liquid rubber obtained by decreasing the molecular weight of natural rubber, and does not have an object to modify a polymer by performing recombination of a main chain structure while controlling a molecular weight.
Attempt is made to modify wet grip performance (hereinafter sometimes referred to as “wet performance”), low fuel consumption performance (rolling resistance) and the like of a tire by operating polarity by grafting onto a polymer, modification of a terminal, addition of a functional group, and the like as described above (for example, PTLs 1 and 4). Modification such as grafting onto a polymer, addition of a functional group and the like has the effect to increase a grass transition point (Tg), and concurrently is a method of improving low fuel consumption performance by an interaction between the functional group and a filler.
However, wet performance and low fuel consumption performance of a tire are originally performances to be antinomic, it is difficult to greatly improve those performances simultaneously, and sufficient result is not yet obtained.
On the other hand, a rubber after vulcanization has problems of deterioration of a crosslinked structure by heat, light or deformation, and deformation by the deterioration, and various attempts are made for the improvement. In particular, improvement of reversion in natural rubber and improvement of interaction between natural rubber and a filler are required, and in addition to this, improvement of low fuel consumption performance, and the like are also required. To improve deterioration of a rubber after vulcanization as describe above, for example, introduction of chemicals suppressing deterioration of an age resister and the like, and adjustment of vulcanization components such as sulfur and accelerator, and a crosslinking agent are conducted as the means of improving heat and light decomposition of polymer components, and decomposition and change of a sulfur crosslinked structure (for example, PTL 2).
However, there is no example that the problem of deterioration of a rubber after vulcanization has been solved by grafting onto a polymer, modification of a terminal, addition of a functional group, and the like.